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Dave H

Whiskey mash stuck in ferment.

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I am a newbie so bear with me... I have started a 5G whiskey mash, 77% flaked corn,  10% distillers malt, 13% flaked rye.  I used a small bullet blender to mill the malt.  I mashed in a 6.5 gallon kettle for the appropriate times (corn for 60 minutes, then malt and rye for 90 min)... let rest overnight.  the next day I pitched 10g of nutrient and 20g of yeast at about 92 degrees (I did not rehydrate the yeast). I left the mash ON the grain.  I stirred for quite a while, hopefully enough to agitate and aerate the mash adequately.  I measured an original specific gravity of 1.077 temperature corrected for about 86 degrees.  Then I placed in a fermentation chamber that I keep at a perfect 78 degrees.  It may fluctuate from 76-82 degrees but my mash always measures about 77-78 degrees when I check temp.  I also keep it in a 6.5G brew bucket with an airlock.  

SO... after 3 hours I checked the airlock and had no activity but I did not worry.  I waited another 24 hours.  Then I checked and there was no activity BUT I measured SG to be about 1.062 so I assumed all was well.  After another 24 hours I measured SG at 1.060... that's when I began to worry.  then after another 24 hours it STILL measured 1.060.  So I reached out for some advice and after some consideration I decided to give it a good stir and repitch some rehydrated yeast (oh btw I use Red Star DADY).  I got some action through the airlock after that (assuming I just released some trapped CO2) but after three more days I was only down to 1.055.  Is my mash DONE?  Wouldn't that only be about 2.9% yield?  Was I being too hopeful to think I would have a final gravity of closer to 1.02?  

I read an article saying that maybe the malt wasn't enough to finish the sugar conversion and I should reheat the mash and add amylase enzyme then repitch again.  What do you think?

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  1. Temp when you mashed the malt?
  2. Did you happen to take PH readings?

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So on a grain ferment how are you taking gravity Readings.  Refractometer won't be accurate because of presence of alcohol and hydrometer won't be accurate because of presence of solids .

Tim 

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@Hudson bay distillers Tim, I placed a grain bag in the bucket before adding the mash... so to take gravity I just pull from the other side of the grain bag. No solids. 

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@RedFalcon I mashed at 158F. Not sure what the temp was when completed but I am sure it was more than 150F. And I didn’t test ph at the time but it is currently 3.50. I feel like it’s a bit low but it has been sitting for 10 days now

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Dump it on the compost pile, start over.

10 days of bacterial fermentation and a pH of 3.5 has it so chock full of carboxylic acids that the environment will be far too stressful to the yeast to give a good end result, even if you could get it to restart (you probably can't).

For giggles - dose lye to increase pH to 5.2, boil it, dose a "rescue" yeast like EC-1118 with a fairly large pitch, rehydrated, ideally with rehydration nutrient.  Though, if you do get it to ferment to completion, I suspect it will require a fairly massive heads cut, and will yield a pretty funky distillate.  I don't think it's even worth the time.

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@Silk City Distillers what should I do differently?  What did I do wrong? I started a new batch last night. Same mash bill but this time I added 1/2 tsp of amylase enzyme after I got the rye and malt mixed in.  I cooked the corn for 60 minutes @ 167F-158F... then I added rye and malt @ 158F... mashed for 90 minutes... lowest temp was 148F and the highest was 152F.  Now I am letting it rest until it reaches 90F so I can pitch.  It's at about 120F right now.  The only thing I can think of is that a) maybe I should have added amylase last time and/or b) maybe I didn't aerate it enough when i pitched the yeast.     

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@Roger that link just took me to the home distiller forum's main page, not any specific post... unless you're just saying I should post this there?  FYI I post here because I also do commercial distilling, this is a side project.

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I'm guessing your yeast didn't stand a chance. Overnight at low 100s is an ideal temp for lacto, and pitching at 92 without re-hydration you probably didn't have a good population that got out-competed by the lacto. 

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@Tom Lenerz this thread has got me thinking the same thing...  but I have heard of plenty of people who let it sit overnight.  Am I just keeping it too hot?  Would you recommend I use a wort chiller and drop the temp straight to 90 after mashing and go ahead and pitch with rehydrated yeast?  (I'm going to always rehydrate now).  And now the problem I have is that I just did the same thing again last night.  Is there anything I can do to remedy THIS batch?  I know I should have waited for the next batch until I figured out what I was doing wrong but too late now haha.  I figured it was just the amylase enzyme and aerating that was the issue.  Thanks.   

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I would just make sure you have a healthy pitch of yeast at an appropriate temp to try and remedy. The rest overnight might work, but if the bacterial ferment is strong is possible the pH drops too much before the yeast get started, giving them a hard time.

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So I pretty much called this one a wash... But I know what I did wrong now... I hate when people post issues and never follow up so I will follow up.  

I am certain that I did not mash correctly.  I'm actually pretty sure that I mashed at too high of a temp.  I think it may have been over 160F most of the time and that is hot enough to denature (I think that's the term) the amylase enzymes.  I was told they work best from 152F-158F.  So I think with THIS batch I only had a little bit of conversion.  That would explain why SG only dropped a little bit.  

So I started a new batch.  I waited until temp was 156F before adding malt and amylase enzymes... mashed for more than long enough (over 90 minutes for sure... closer to 2 hours)  I checked it with an iodine test (which was tricky because if you swirl it into the mash it does turn blue but when it rests on top it stays an amber color).  Then I pitched nutrient and yeast at 90F.  Within 2 hours she was bubbling every 2 seconds or so.  Within 12 hours my airlock is going nuts.  It looks like a rolling boil in there!

Thanks for your help, everyone!

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Glucoamylase is cheap insurance if you have some concern about mash protocol issues.

Dosing Alpha amylase and mashing in hot - you’ll create a lot of dextrins, not so much sugar.

Distillers typically mash in cooler than brewers.  We don’t care about mouthfeel or residual sugar.  Cooler mash in results in higher wort fermentability.  This is due to creating more favorable conditions for beta amylase.

Glucoamylase will chop up any dextrin that remains.  Ensuring high levels of saccharification.  It will also hydrolyze some of the remaining starch if you are fermenting on grain.

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